This invention relates generally to wet mix concrete mixing machines. More particularly, the present invention is concerned with wet mix machines adapted to process relatively large aggregates.
In my prior patent, U.S. Pat. No. 3,188,059, issued June 8, 1965, I devised a system for producing wet mix concrete in which a pair of rotatable, generally horizontally oriented impeller assemblies are mounted for rotation within a mixing chamber. The chamber is formed from a pair of generally tubular, horizontally disposed pump casings, which share a common, open internal side. The impeller assembly includes spirally formed blades which extend along the outer periphery of the impeller spiders. The blades wipingly contact the inner surfaces of the casings to produce blending of aggregates and materials within the chamber.
A variety of aggregates may be used to prepare a desired cementitious product. These aggregates and/or other materials are generally mixed with water, and a foam may be inputted to trap air in small dispersed pockets generally uniformly throughout the mixture. The foam for the mix may be developed by injecting a liquid detergent, water and air, all under pressure, through conventional nozzles into the mix of aggregates of cement. Typical materials for preparing such mixtures may comprise sand, gravel, and expanded vermiculite, mica or perlite. However, where gravel, or other relatively large aggregates are to be mixed within the cementitious product, problems have heretofore been experienced with the efficiency of my prior design. While the impeller assembly of my previous design accomplishes uniform mixture of generally light weight cementitious materials, becasue of the impeller design, processing of large aggregate materials is impeded since the fine screen mesh in the wiper blade is of insufficient diameter to provide clearance for aggregate particles.
However, as indicated in the specification of the previously mentioned patent, the particular configuration of a pair of horizontally disposed generally spirally formed impeller assemblies, which rotate in opposite directions, adds particular advantages insofar as providing a uniform mix. One of the reasons for the latter phenomena is that as rotation continues, the cementitious materials are uniformly mixed simultaneously with the natural conveyance of the blend towards the discharge of the unit. Increased drag and frictional losses experienced with larger aggregates in my earlier design may interfere with the natural passage of the mixed material toward the discharge orifice. Moreover, when motor power and/or speed are increased to handle large aggregate materials, the mechanical wear and tear on moving parts increases radically, resulting in down time and required repairs. Also, the expense of providing larger motors to handle the increased drag and resistance of larger aggregate materials is prohibitive.
Another problem with my prior art design relates to the handling of the door structure when discharging materials containing large aggregate. The previous sliding type design has been found insufficient since large diameter aggregate particles tend to jam the door and prevent its efficient operation. On the other hand, it is nevertheless required to provide easily operable mechanical means for manually moving the door between unobstructed open positions and reliably sealed positions.